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Solution - Absolute value equations

Exact form:

z = - \frac{5}{2}

z=-\frac{5}{2}

Mixed number form:

z = - 2 \frac{1}{2}

z=-2\frac{1}{2}

Decimal form:

z = - 2.5

z=-2.5

See steps

Step-by-step explanation

1. Rewrite the equation without absolute value bars

Use the rules:
$| x | = | y |$ → $x = \pm y$ and $| x | = | y |$ → $\pm x = y$
to write all four options of the equation
$| z + 9 | = | z - 4 |$
without the absolute value bars:

$\| x \| = \| y \|$	$\| z + 9 \| = \| z - 4 \|$
$x = + y$	$(z + 9) = (z - 4)$
$x = - y$	$(z + 9) = - (z - 4)$
$+ x = y$	$(z + 9) = (z - 4)$
$- x = y$	$- (z + 9) = (z - 4)$

When simplified, equations $x = + y$ and $+ x = y$ are the same and equations $x = - y$ and $- x = y$ are the same, so we end up with only 2 equations:

$\| x \| = \| y \|$	$\| z + 9 \| = \| z - 4 \|$
$x = + y$ , $+ x = y$	$(z + 9) = (z - 4)$
$x = - y$ , $- x = y$	$(z + 9) = - (z - 4)$

2. Solve the two equations for z

5 additional steps

$(z + 9) = (z - 4)$

Subtract from both sides:

$(z + 9) - z = (z - 4) - z$

Group like terms:

$(z - z) + 9 = (z - 4) - z$

Simplify the arithmetic:

$9 = (z - 4) - z$

Group like terms:

$9 = (z - z) - 4$

Simplify the arithmetic:

$9 = - 4$

The statement is false:

$9 = - 4$

The equation is false so it has no solution.

10 additional steps

$(z + 9) = - (z - 4)$

Expand the parentheses:

$(z + 9) = - z + 4$

Add to both sides:

$(z + 9) + z = (- z + 4) + z$

Group like terms:

$(z + z) + 9 = (- z + 4) + z$

Simplify the arithmetic:

$2 z + 9 = (- z + 4) + z$

Group like terms:

$2 z + 9 = (- z + z) + 4$

Simplify the arithmetic:

$2 z + 9 = 4$

Subtract from both sides:

$(2 z + 9) - 9 = 4 - 9$

Simplify the arithmetic:

$2 z = 4 - 9$

Simplify the arithmetic:

$2 z = - 5$

Divide both sides by :

$\frac{(2 z)}{2} = \frac{- 5}{2}$

Simplify the fraction:

$z = \frac{- 5}{2}$

3. Graph

Each line represents the function of one side of the equation:
$y = | z + 9 |$
$y = | z - 4 |$
The equation is true where the two lines cross.

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Why learn this

We encounter absolute values almost daily. For example: If you walk 3 miles to school, do you also walk minus 3 miles when you go back home? The answer is no because distances use absolute value. The absolute value of the distance between home and school is 3 miles, there or back.
In short, absolute values help us deal with concepts like distance, ranges of possible values, and deviation from a set value.

Solution - Absolute value equations

Step-by-step explanation

1. Rewrite the equation without absolute value bars

2. Solve the two equations for z

3. Graph

Why learn this

Terms and topics

Related links

Solution - Absolute value equations

Step-by-step explanation

1. Rewrite the equation without absolute value bars

2. Solve the two equations for z

3. Graph

Why learn this

Terms and topics

Related links

Latest Related Drills Solved